QDD shoulder
High torque is placed at the joint that carries the most load.
Good Enough Manipulator
GEM
A useful humanoid arm for hobbyists and researchers: 7 DOF, up to 1.2 kg payload, 3D printed structure, and a target build cost under $500.
7DOF
1.2 kgpayload
<$500arm BOM
$120leader arm
Why it exists
Low cost. Real work.
SO-100 introduced thousands of people to robotics, but its 5 DOF layout, roughly 450 g payload, and limited precision make many research tasks hard. GEM keeps the open, accessible spirit while adding the payload, reach, cameras, and control stack needed for data collection and policy training.
Motor layout
Payload where it counts.
A high-torque QDD shoulder carries the heavy lifting, while lower-cost Feetech servos handle the elbow, wrist, and gripper. Concentrating torque near the base keeps the moving mass low and makes the rest of the arm much cheaper without giving up useful payload.
Strong mid-arm servos
STS3095 and STS3250 joints handle reach and lifting without dominating cost.
Light distal joints
STS3215 servos keep the wrist and gripper compact, cheap, and responsive.
Live model
Live 3D arm
Inspect the printed structure, joint layout, and camera mounts before you build. The model reflects the released geometry, including the mounting positions you will assemble around.
PayloadUp to 1.2 kg
Motion7 degrees of freedom
FabricationFully 3D printed structure
SensingHead and wrist cameras
TeleopLeader arm, VR joystick, phone
TrainingLeRobot VLA pipeline
Tasks
Harder tasks, cheaper arm.
Payload
Move heavier objects with useful torque where it matters.
Dexterity
Stack, insert, grasp, and recover with 7 DOF.
Leader control
A $120 leader arm for precise dataset collection.
Alternate teleop
Use VR joystick or phone control when that fits better.
Control stack
Runs on LeRobot.
Use the GEM branch of Joeclinton1/lerobot for motor calibration, teleoperation, camera capture, and policy training.
1. Install the fork
git clone https://github.com/Joeclinton1/lerobot
cd lerobot
git switch gem
pip install -e .2. Configure hardware
Use the GEM follower robot implementation in
src/lerobot/robots/gem_follower, then calibrate motors and cameras.
3. Collect and train
Record head and wrist camera data with the leader arm, then train pi0.5 or another LeRobot policy from the standardized camera setup.
Print files
Download the parts.
Start with the all-parts 3MF if you want the quickest print setup. The STL packs split the arm, mount, and leader so you can reprint only the pieces you need. Source STEP files are included for inspection and modification.
All arm parts
Single prepared print file for the main GEM arm parts.
DownloadArm STLs
Main arm structure plus the PincOpen gripper print files.
DownloadMount STLs
Base, electronics mount, E-stop clamp, and head-camera mount.
DownloadLeader STLs
Leader arm parts and matching leader mount files.
DownloadSource CAD
Public assembly STEP files with the GEM and PincOpen license notices.
DownloadGEM design files are CC BY-NC-SA 4.0. PincOpen files from Pollen Robotics stay under their original CC BY-SA 4.0 license and are marked in the downloads.
Build manual
Build it step by step.
Follow the arm from printed parts to a wired robot. Each step pairs the action with a render so part orientation and insertion direction are easy to check.
Bill of materials
Parts and cost.
The core arm is designed around widely available motors, bearings, fasteners, wiring, and printed structure so the build stays practical to source.
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